According to Hartsink's history of Guyana (see under documentation), the 'island of Mecoria' was the site of a Dutch coloy from 1634 tot 1636, which had been founded on the private initiative of Jan Bicker, without the consent of the WIC. The Dutch found an abandoned French fortification there, which they restored and used during their short-lived presence in the area.
In this description, Mecoria is situated between the Cayenne and Wia rivers (the latter probably denoting the Mahury), i.e. east of the Cayenne river. Interestingly, the region of the west bank of the Cayenne is still called Macouria.